Field of the Invention
The present invention relates to a display device and, more particularly, to a display device capable of low-speed driving and a method of driving the same.
Discussion of the Related Art
Display devices are used in a variety of display products, such as portable information devices, office appliances, computers, and televisions. The PSR (Panel Self Refresh) technology is known to reduce power consumption in display devices. The PSR was suggested to improve system power saving performance. It minimizes power consumption using a frame memory incorporated in a display module. When a PSR feature is activated, the system stores a still image data in the display module's frame memory. The system's operating power is cut off until a new still image data is input. With the power cut off, the data stored in the frame memory is repeatedly displayed. As such, power consumption is reduced without the user recognizing it.
The PSR technology was originally suggested for still images, but there have been recent attempts to extend the application of this technology to moving video images. An example of such attempts is the PSR-based 24 FPS (Frame Per Second) image display technology.
For video images, FPS (Frame Per Second) indicates the amount of image data transmitted from the host system to the display module for 1 second. FPS is distinguished from frame frequency, which is the rate at which the screen on the display module refreshes. FPS and frame frequency may vary. For example, as shown in FIG. 1, a 24 FPS video consisting of 24 different frames may be displayed on the display module running at a frame frequency of 60 Hz. In this case, 24 fps images are displayed through 60 frames in such a manner that the first fps image is repeated in the first to the third frames, and the second fps image is repeated in the fourth and the fifth frames. The system's operating power is cut off in 36 of the 60 frames, not including the 24 frames in which the 24 fps images are respectively transmitted to the display module.
The PSR technology can work with a low-speed driving technique that is implemented through interlaced driving. Interlaced low-speed driving can reduce the output frame frequency to one half or less of the input frame frequency by increasing the refresh cycle of the image data to at least two frames. FIG. 2 shows an example of interlaced low-speed driving, in which some gate lines, e.g., G1, G2, G5, and G6, are driven (odd scanning of FIG. 2) in odd frames and the other gate lines, e.g., G3, G4, G7, and G8, are driven (even scanning of FIG. 2) in even frames. As a result, in this example, an image data input in synchronization with an input frame frequency of 60 Hz is displayed at an output frame frequency of 30 Hz.
However, in the event that interlaced low-speed driving is performed for video images synchronized with the PSR, display distortion caused by data inconsistency may result in particular frames in which an image data different from that of the preceding frame is written. For example, if image data A to be written in the third frame is different from image data B to be written in the fourth frame as shown in FIG. 2, the displayed image made up partly from the image data A and partly from the image data B becomes distorted in the fourth frame.
Due to this display distortion, the related art devices are not capable of implementing interlaced low frequency driving with respect to video image data synchronized with the PSR. Instead, they implement only normal driving (at the output frame frequency of 60 Hz, which is the same as the input frame frequency) as shown in FIG. 1. As a result, there is a limitation in the related art with respect to reducing power consumption.